Synchronization of Mobile Client Multicast Membership

ABSTRACT

Synchronization of mobile multicast membership in a wireless network. A controller supports one or more wireless access points, each of which supports wireless clients. A Mobility Manager (MM) in the controller monitors wireless client activity. The controller establishes an IGMP proxy which intercepts IGMP messages from wireless clients and handles the IGMP messages on clients&#39; behalf. When a wireless client wishes to join a multicast, the client&#39;s IGMP join message is intercepted by the controller IGMP proxy, and the controller IGMP proxy joins the multicast for the client. The Mobility Manager observes the actions of the IGMP proxy. If a client moves from its home agent (HA) controller to a different foreign agent (FA) controller, the Mobility Manager in the FA controller locates the Mobility Manager in the HA controller and receives information on the client including information on any multicast streams the client is receiving. The Mobility Manager in the FA controller uses this information to have its own IGMP proxy join the required multicast, and send the multicast stream to the client.

BACKGROUND OF THE INVENTION

The present invention relates to wireless systems, and in particular, tothe problem of synchronizing multicast data streams to mobile clients inthe wireless environment.

Modern wireless systems operating under IEEE 802.11 standards are calledupon to support a wide range of clients operating over a wide range ofdata rates, using different modulation types, and different protocols.

The users of these networks see, or desire to see a set of services,available on demand, wherever they are. They expect these services tooperate reliably, and continue to operate as they move, for example,from one area to another in an office environment, or from one buildingor floor to another in a corporate campus.

Broadcast/multicast (BCMC) traffic in an 802.11 wireless network belongsto a single broadcast domain, such as one or more wireless access nodesconnected to a controller. This BCMC traffic cannot be leaked or sharedacross multiple different domains. This BCMC traffic is usually managedaccording through the well known Internet Group Management Protocol(IGMP) as defined for example in RFC 1112 (IGMP V1), RFC 2236 (IGMP V2)and RFC 3376 (IGMP V3), each incorporated herein by reference.

When a mobile client crosses a Layer 3 (L3) boundary, for example movingfrom an area covered by one controller and its wireless access nodes toan area covered by a different controller and its wireless access nodes,existing protocols allow the wireless client to retain its IP address.

But the BCMC traffic to and from the client is restricted to a singlebroadcast domain. When the mobile client crosses a L3 boundary, theseBCMC sessions are dropped until the client rejoins these BCMC sessions.

What is needed is a way to maintain multicast membership and sessions aswireless clients move across boundaries.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention in which:

FIG. 1 shows a wireless 802.11 network.

DETAILED DESCRIPTION

Embodiments of the invention relate to methods of synchronizing mobileclient multicast membership in wireless data networks. According to anaspect of the invention, a controller supports one or more wirelessaccess nodes, the access nodes supporting wireless clients. A MobilityManager (MM) in the controller monitors the activity of the wirelessclients. When a wireless client attempts to join a multicast group usingan IGMP multicast join, an IGMP proxy in the controller intercepts theseIGMP control messages, joining the multicast group for the client, andestablishing itself as the client's home agent (HA). This activity istracked by the Mobility Manager. Subsequent IGMP messages from that orother clients on the controller are handled by the IGMP proxy acting ontheir behalf, and are also tracked by the Mobility Manager. The IGMPproxy in the controller performs joins and acts as a host for each BCMCclient of its wireless access nodes.

When a client moves from its home agent (HA) controller to a foreignagent (FA) controller, downstream multicast traffic for the client isstill received by the IGMP proxy at the HA. The Mobility Manager in theFA contacts the Mobility Manager in the HA and receives information onany active multicast traffic associated with the client; the MobilityManger in the FA then establishes those multicast connections for theclient through its own IGMP proxy, which forwards the multicast streamsto the client.

As shown in FIG. 1, a wireless network operating according to 802.11standards supports connections of wireless clients 400 to a wirednetwork. Wired network 100, such as a wired IEEE 802.3 Ethernet network,is connected to layer 3 router 150, which supports controllers 200 a,200 b. Controllers 200 support connections 250 to access nodes 300 a,300 b, 300 c. These access nodes provide wireless communications towireless clients such as wireless client 400.

As is understood in the art, controllers 200 are a purpose-built digitaldevices having a CPU 210, memory hierarchy 220, and a plurality ofnetwork interfaces 230, 240. CPU 210 may be a MIPS-class processor fromcompanies such as Raza Microelectronics or Cavium Networks, althoughCPUs from companies such as Intel, AMD, IBM, Freescale, or the like mayalso be used. Memory hierarchy 220 includes read-only memory for devicestartup and initialization, high-speed read-write memory such as DRAMfor containing programs and data during operation, and bulk memory suchas hard disk or compact flash for permanent file storage of programs anddata. Network interface 230 is typically an IEEE 802.3 Ethernetinterface to copper, although high-speed optical fiber interfaces mayalso be used. Controller 200 typically operates under the control ofpurpose-built embedded software, typically running under a Linuxoperating system, or an operating system for embedded devices such asVXWorks. Network interface 240 is typically a wireless interfaceoperating under IEEE 802.11 standards.

Similarly, as understood by the art, wireless access nodes 300 a, 300 band 300 c, are also purpose-built digital devices. These access nodesinclude CPU 310, memory hierarchy 320, wired interface 330, and wirelessinterface 340. As with controller 200, the CPU commonly used for suchaccess nodes is a MIPS-class CPU such as one from Raza Microelectronicsor Cavium Networks, although processors from other vendors such asIntel, AMD, Freescale, and IBM may be used. The memory hierarchycomprises read-only storage for device startup and initialization, fastread-write storage such as DRAM for holding operating programs and data,and permanent bulk file storage such as compact flash. Wireless accessnodes 300 typically operate under control of purpose-built programsrunning on an embedded operating system such as Linux or VXWorks.Wireless interface 340 is typically an interface operating to the familyof IEEE 802.11 standards including but not limited to 802.11a, b, g,and/or n.

Wireless client 400 is also a digital device, similarly having CPU 410,memory hierarchy 420, wireless interface 430, and I/O devices 440. Asexamples, wireless device 500 may be a general purpose computer such asa laptop, or may be a purpose-built device such as a Wi-Fi phone or ahandheld scanner. In a general-purpose computer, CPU 410 may be aprocessor from companies such as Intel, AMD, Freescale, or the like. Inthe case of purpose-built devices, Acorn or MIPS class processors may bepreferred. Memory hierarchy 420 comprises the similar set of read-onlymemory for device startup and initialization, fast read-write memory fordevice operation and holding programs and data during execution, andpermanent bulk file storage using devices such as flash, compact flash,and/or hard disks. Additional I/O devices 440 may be present, such askeyboards, displays, speakers, barcode scanners, and the like.

According to an aspect of the invention, Mobility Manager (MM) 270operates in controller 200 a, monitoring the activity of connectedwireless clients. Assuming client 400 is connected to controller 200 athrough access node 300 a, when wireless client 400 issues an IGMPcontrol message, this IGMP control message is intercepted by controller200 a. If an IGMP proxy process 250 does not exist on controller 200 a,one is started. This IGMP Proxy 250 will trap and handle all IGMPmessages from wireless clients of controller 200 a, and act in theirbehalf.

As an example, if client 400 sends an IGMP join to join a multicast,IGMP Proxy 250 on controller 200 a will trap this request, and then sendits own IGMP join request upstream, joining the multicast as a proxy forclient 400. The IGMP Proxy on controller 200 a can act as a host forother wireless clients wishing to join the same (or a different)multicast.

The activity of IGMP Proxy 250 is monitored by Mobility Manager 270. Asis understood by the art, this may be through the use of shared datastructures or other software methods whereby Mobility Manager 270 tracksthe activities of client 400 including any activity of client 400through IGMP proxy 250. It is understood that Mobility Manager 270 is asoftware process running in controller 200. Mobility Manager 270 may bewritten in any number of different computer languages such as C or C++,depending on the implementation requirements of the other softwarecomponents of the controller.

If client 400 moves to a different wireless access node and controller,for example controller 200 b through access node 300 c, downstreamunicast traffic for client 400 will be forwarded to client 400 throughthe new controller 200 b. Multicast traffic, however, is not forwarded.

According to an aspect of the invention, when client 400 roams from homeagent (HA) controller 200 a to foreign agent (FA) controller 200 b, theMobility Manager 270 in FA controller 200 b sends queries to MobilityManagers 270 in all controllers 200 in its mobility domain to determinethe HA controller for client 400. When the Mobility Manager 270 incontroller 200 a identifies itself as the HA for client 400, theMobility Manager 270 in HA controller 200 a sends information toMobility Manager 270 in FA controller 200 b, including information onany open IGMP multicasts being handled for client 400 through the IGMPproxy 250 in HA 200 a. Mobility Manager 270 in FA controller 200 b thenuses this information with its own IGMP proxy to join the requiredmulticasts and send the multicast traffic to client 400.

This process is facilitated by having the IGMP proxy 250 in eachcontroller 200 keep multicast databases of the clients 400 it serves andsharing this information with the Mobility Manager in the controller.When a client roams from its home agent to a foreign agent, the MobilityManager in the foreign agent locates the home agent and receivesinformation from the Mobility Manager in the home agent, includinginformation on active multicast streams for the client.

While the invention has been described in terms of various embodiments,the invention should not be limited to only those embodiments described,but can be practiced with modification and alteration within the spiritand scope of the appended claims. The description is this to be regardedas illustrative rather than limiting.

1. A method of operating a packet-switched digital network having aplurality of controllers forming a mobility domain, each controllerhaving at least one access node for supporting wireless clients,comprising: an IGMP proxy in each controller supportingbroadcast/multicast sessions to wireless clients connected to thecontroller through the at least one access node, a mobility manager ineach controller monitoring the open broadcast/multicast sessions carriedby the IGMP Proxy, the mobility manager detecting when a client hasroamed to an access node connected to its controller, the mobilitymanager sending inquiries to the mobility managers in other controllersin the mobility domain for information on active broadcast/multicastsessions for the roamed client, if the mobility manager receivesinformation from another mobility manager in the mobility domaincontaining information on open broadcast/multicast sessions for theroamed client, forwarding this information to the IGMP proxy in thecontroller to establish those broadcast/multicast sessions for theroamed client.
 2. The method of claim 1 where the mobility manager inthe controller responds to requests from other mobility managers in themobility domain.
 3. The method of claim 2 where the mobility managerresponds to requests from other mobility managers in the mobility domainwith information on wireless clients attached to the controller hostingthe mobility manager.
 4. The method of claim 2 where the mobilitymanager responds to requests from other mobility managers in themobility domain with information on open broadcast/multicast streams forwireless clients attached to the controller hosting the mobilitymanager.
 5. The method of claim 2 where the mobility manager responds torequests from other mobility managers in the mobility domain withinformation on a specific wireless client attached to the controllerhosting the mobility manager.
 6. The method of claim 5 where theinformation on the specific client includes information on any openbroadcast/multicast sessions for the specific client.
 7. A controlleroperating in a packet-switched digital network that comprises aplurality of controllers forming a mobility domain and including atleast one access node for supporting wireless clients, the controllercomprising: an IGMP proxy to support broadcast sessions to one or morewireless clients in communication with the controller through the atleast one access node; and a mobility manager to monitor the openbroadcast sessions carried by the IGMP Proxy, the mobility managerdetecting when a client has roamed to an access node connected to thecontroller, sending inquiries to a second mobility manager in anothercontroller of the plurality of controllers in the mobility domain forinformation on active broadcast sessions for the roamed client, whereinif the mobility manager receives information from the second mobilitymanager in the mobility domain containing information on open broadcastsessions for the roamed client, forwarding this information to the IGMPproxy in the controller to establish those broadcast sessions for theroamed client.
 8. The controller of claim 7 where the mobility managerresponds to requests from other mobility managers in the mobilitydomain.
 9. The controller of claim 8 where the mobility manager respondsto requests from the other mobility managers in the mobility domain withinformation on wireless clients attached to the controller hosting themobility manager.
 10. The controller of claim 8 where the mobilitymanager responds to requests from the other mobility managers in themobility domain with information on open broadcast streams for wirelessclients attached to the controller hosting the mobility manager.
 11. Thecontroller of claim 8 where the mobility manager responds to requestsfrom the other mobility managers in the mobility domain with informationon a specific wireless client attached to the controller hosting themobility manager.
 12. The controller of claim 11 where the informationon the specific client includes information on any open broadcastsessions for the specific client.
 13. A controller operating in apacket-switched digital network that comprises a plurality ofcontrollers forming a mobility domain and including at least one accessnode for supporting wireless clients, the controller comprising: an IGMPproxy to support multicast sessions to one or more wireless clients incommunication with the controller through the at least one access node;and a mobility manager to monitor the open multicast sessions carried bythe IGMP Proxy, the mobility manager detecting when a client has roamedto an access node connected to the controller, sending inquiries to asecond mobility manager in another controller of the plurality ofcontrollers in the mobility domain for information on active multicastsessions for the roamed client, wherein if the mobility manager receivesinformation from the second mobility manager in the mobility domaincontaining information on open multicast sessions for the roamed client,forwarding this information to the IGMP proxy in the controller toestablish those multicast sessions for the roamed client.
 14. Thecontroller of claim 13 where the mobility manager responds to requestsfrom other mobility managers in the mobility domain.
 15. The controllerof claim 13 where the mobility manager responds to requests from theother mobility managers in the mobility domain with information onwireless clients attached to the controller hosting the mobilitymanager.
 16. The controller of claim 13 where the mobility managerresponds to requests from the other mobility managers in the mobilitydomain with information on open multicast streams for wireless clientsattached to the controller hosting the mobility manager.
 17. Thecontroller of claim 13 where the mobility manager responds to requestsfrom the other mobility managers in the mobility domain with informationon a specific wireless client attached to the controller hosting themobility manager.
 18. The controller of claim 17 where the informationon the specific client includes information on any open multicastsessions for the specific client.